Refrigerating unit

ABSTRACT

A refrigerating unit capable of optimum operation with respect to load by finely changing the operating capacity in response to changes in load, and offering energy saving effects. The refrigerating unit has a scroll type inverter-driven compressor and scroll type constant-speed compressors; a pressure sensor installed on the suction side; a circuit for starting the inverter-driven compressor first; and a circuit for deciding the driving frequency of the compressor and the number of constant-speed compressors to operate, based on a suction pressure value detected by the pressure sensor after the compressor was started.

BACKGROUND OF THE INVENTION

The present invention relates to a refrigerating unit which has aplurality of compressors installed in parallel and controls theoperation capacity according to the load to be refrigerated, and thisrefrigerating unit is most suitable to a configuration that includes aninverter-driven compressor and constant-speed compressors.

In refrigerating units incorporating an inverter-driven compressor andconstant-speed compressors, it has been known to additionally put theconstant-speed compressor into operation and reduce the drivingfrequency of the inverter-driven compressor when the driving frequencyof the inverter-driven compressor has reached the maximum value and theload further increases. In conjunction with this, a method worthy tonote here has been disclosed in JP-A-09-273819, in which when switchingover the operation from the inverter-driven compressor to theconstant-speed compressor, the inverter-driven compressor is brought toa halt for a fixed period of time to decrease the operation time of theinverter-driven compressor to thereby improve the reliability of theinverter-driven compressor.

Since in the prior art mentioned above the driving frequency of theinverter-driven compressor is lowered or the inverter-driven compressoris stopped from operating for a fixed period in response to changes inload, it has been difficult to finely control the operation capacity inresponse to varying load, and there has been a possibility that the loadcapacity and the operation capacity become unmatched.

The object of the present invention is to make it possible to finelyvary the operation capacity in response to changes in load, enableoptimum operation according to load, and thereby achieve a reduction inenergy consumption.

SUMMARY OF THE INVENTION

According to an aspect of the present invention made to achieve theabove object, in a refrigerating unit having an inverter-drivencompressor using a variable driving frequency, and constant-speedcompressors using a constant driving frequency, the refrigerating unitcomprising a pressure sensor installed on the suction side of theinverter-driven compressor and constant-speed compressors, means forstarting the inverter-driven compressor first, and means for deciding adriving frequency for the inverter-driven compressor or deciding thenumber of compressors to operate, based on a suction pressure valuedetected by the pressure sensor after the inverter-driven compressor isstarted.

Because the operation of the inverter-driven compressor is startedfirst, it is possible to obtain a smooth starting of the operation ofthe refrigerating unit in accordance with load when the unit is started.After this, the driving frequency of the inverter-driven compressor orthe number of compressors to operate is decided based on the suctionpressure value of the compressors. Therefore, even if there is a greatchange in refrigerating load, a sufficient capacity can be secured inaccordance with this great change of load, and the capacity can befinely controlled. Thus, it is possible to perform the operation withoptimum operation capacity with respect to load and thereby reduceenergy consumption.

In the above operation, when the suction pressure value rises above aspecified value, it is desirable to start one or more constant-speedcompressors regardless of the driving frequency of the inverter-drivencompressor.

Further in the above operation, when the suction pressure value fallsbelow a specified value, it is desirable to stop the constant-speedcompressors regardless of the driving frequency of the inverter-drivencompressor.

Further in the above operation, it is desirable to start theconstant-speed compressors one by one after the driving frequency of theinverter-driven compressor has reached the maximum value.

Further in the above operation, it is desirable to stop theconstant-speed compressors one by one after the driving frequency of theinverter-driven compressor has reached the minimum value.

Further in the above operation, it is desirable to decide the maximumand minimum values of the driving frequency of the inverter-drivencompressor, start the constant-speed compressors one by one after themaximum frequency has been reached, and stop the constant-speedcompressors one by one after the minimum frequency has been reached.

According to another aspect of the present invention, in a refrigeratingunit having an inverter-driven compressor using a variable drivingfrequency, and constant-speed compressors using a constant drivingfrequency, the refrigerating unit comprising an inverter-drivencompressor of scroll type and constant-speed compressors of scroll type,and a pressure sensor installed on the suction side of theinverter-driven compressor and constant-speed compressors, and when avalue detected by the pressure sensor at the start of the operation isgreater than a preset value, an inverter-driven compressor and aconstant-speed compressor are started, and thereafter the drivingfrequency of the inverter-driven compressor and the number ofconstant-speed compressors to operate are decided.

Because the inverter-driven compressor and a constant-speed compressorsare started when the suction pressure value of the compressors isgreater than a preset value at the start of the operation, a sufficientoperation capacity relative to load can be secured at the start of theoperation, and even if there is a sudden increase in load, a smoothstarting can be obtained in response to this sudden load increase.

Thereafter, the driving frequency of the inverter-driven compressor andthe number of constant-speed compressors to operate are decided based ona suction pressure value of the compressors. In consequence, asufficient capacity can be secured according to load and fine control ofcapacity can be realized.

According to a further aspect of the present invention, in arefrigerating unit having an inverter-driven compressor using a variabledriving frequency, and constant-speed compressors using a constantdriving frequency, the refrigerating unit comprising an inverter-drivencompressor of scroll type and constant-speed compressors of scroll type,and a pressure sensor installed on the suction side of theinverter-driven compressor and constant-speed compressors, and thedriving frequency of the inverter-driven compressor and the number ofconstant-speed compressors to operate are decided based on a suctionpressure value detected by the pressure sensor, and the capacity can becontrolled in a wide range of 15% to 100%.

Because the driving frequency of the inverter-driven compressor and thenumber of constant-speed compressors to operate are decided based on asuction pressure value and the capacity control range is from 15% to100%, an optimum operation capacity with respect to conceivable load ofan air conditioner can be obtained, which makes it possible to achieve areduction in energy consumption.

According to an additional aspect of the present invention, in arefrigerating unit having an inverter-driven compressor using a variabledriving frequency, and constant-speed compressors using a constantdriving frequency, the refrigerating unit comprising an inverter-drivencompressor of scroll type and constant-speed compressors of scroll type,a pressure sensor installed on the suction side of the inverter-drivencompressor and constant-speed compressors, means for deciding a drivingfrequency of the inverter-driven compressor and the number of theconstant-speed compressors to operate, based on a suction pressure valuedetected by the pressure sensor, and means for determining a failure ofthe inverter for driving the inverter-driven compressor, and when theinverter is determined to be out of order by the failure-determiningmeans, capacity control is continued by changing the number ofcompressors to operate, including the inverter-driven compressor and theconstant-speed compressors.

Even when the inverter is faulty, the capacity control is continued bychanging the number of compressors to operate, including theinverter-driven compressor and the constant-speed compressors. Thusstepwise capacity control can be continued even if frequency control isnot performed.

According to yet another aspect of the present invention, in arefrigerating unit having an inverter-driven compressor using a variabledriving frequency and constant-speed compressors using a constantdriving frequency, the refrigerating unit comprising an inverter-drivencompressor of scroll type and constant-speed compressors of scroll type,a pressure sensor installed on the suction side of the inverter-drivencompressor and constant-speed compressors, means for starting theoperation of the inverter-driven compressor first when a suctionpressure value (Ps) detected by the pressure sensor is greater than apreset value (PsU), means for decreasing the driving frequency of theinverter-driven compressor according to a difference between the suctionpressure value (Ps) and the preset value (PsU) when the suction pressurevalue has risen above a specified value (C) after the inverter-drivencompressor is started, and means for starting a constant-speedcompressor after the driving frequency is decreased.

Because the operation of an inverter-driven compressor is started firstwhen the suction pressure value (Ps) is greater than a preset value andthe driving frequency of the inverter-driven compressor is decreasedaccording to a difference between the suction pressure value (Ps) and apreset value (PsU) when the suction pressure value has risen above aspecified value (C) and a constant-speed compressor is started when thedriving frequency has been decreased, a change in the operation capacitycan be made small even if the number of compressors operated is changedand therefore a sufficient capacity can be secured with respect tochanges in load and even finer capacity control can be implemented.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a refrigerating cycle flow diagram of a refrigerating unitaccording to an embodiment of the present invention,

FIG. 2 is an operation flow chart in an inverter-driven compressor ofthe refrigerating unit according to the embodiment of the presentinvention,

FIGS. 3A and 3B are operation flow charts in a constant-speed compressorof the refrigerating unit according to the embodiment of the presentinvention,

FIG. 4 is an operation flow chart in the constant-speed compressor ofthe refrigerating unit according to the embodiment of the presentinvention,

FIGS. 5A, 5B and 5C are operation flow charts in the constant-speedcompressor of the refrigerating unit according to the embodiment of thepresent invention,

FIG. 6 is a graph showing operation control zones of a compressor in therefrigerating unit according to the embodiment of the present invention,

FIG. 7 is a block diagram according to the embodiment of the presentinvention, and

FIG. 8 is an operation flow chart of the constant-speed compressoraccording to the embodiment of the present invention.

DESCRIPTION OF EMBODIMENT

An embodiment of the present invention will be described with referenceto the accompanying drawings.

FIG. 1 is a diagram showing an example of a basic refrigerating cycle ofa refrigerating unit according to an embodiment of the presentinvention. In FIGS. 1, 1 a, 1 b and 1 c denote scroll compressors, inwhich 1 a denotes an inverter-driven compressor, and 1 b and 1 c denoteconstant-speed compressors. A refrigerating cycle is formed by thosecompressors and other main devices, such as a condenser 2, a liquidreceiver 3, an expansion valve 4, and an evaporator 5. A pressure sensor6 is mounted on a pipe on the suction side of the compressors, and asuction pressure value detected by the pressure sensor 6 is processed bya unit controller 7 to decide the then operation capacity.

The unit controller 7 controls revolution speed and the number of scrollcompressors to operate by outputting to an inverter 8 an operatingfrequency command for the compressor la and outputting to a multicontroller 9 an operation command for the constant-speed compressors 1 band 1 c, to thereby obtain an optimum operation capacity to suit thethen load capacity.

Referring to FIGS. 2 to 6, description will be made of a method forcontrolling the capacity of the scroll compressors 1 a, 1 b and 1 c.

FIG. 2 is an operation flow chart of the refrigerating unit according toan embodiment of the present invention, chiefly dealing with aninverter-driven compressor controlled by the inverter 8. FIGS. 3A, 3B, 4and 5A-5C are operation flow charts of the constant-speed compressors 1b and 1 c controlled by the multi controller 9. FIG. 4 shows a relationbetween symbols A to F in FIGS. 2, 3A, 3B, 4 and 5A-5C and suctionpressures, and indicates the operation control zones of the compressors1 a, 1 b and 1 c.

Description will start with the operation flow chart of the compressor 1a controlled by the inverter 8.

Before starting the compressor, if the suction pressure Ps detected bythe pressure sensor 6 is greater than a preset start condition value PsUof the compressor 1 a, in other words, if the suction pressure Ps is ina zone from A to C in FIG. 6, the unit controller 7 outputs an operationcommand to the inverter 8 to start the operation of the compressor 1 a.As for the operating frequency at startup, the compressor 1 a is startedat a lower limit frequency of 30 Hz, for example, of the presetoperating frequency range.

After this, when Ps is detected by the pressure sensor 6 and Ps ishigher than PsU, that is to say, when the load is greater than theoperation capacity, the unit controller 7 issues an operating frequencycommand to the inverter 8 to increase the operating frequency. Note thatthe upper limit of the operating frequency is to be the upper-limitfrequency of the preset operating frequency range, 80 Hz for example.

Next, the inverter 8 controls the scroll compressor 1 a to increase itsrevolution speed at a frequency specified by the unit controller 7.

If Ps is less than PsD, that is to say, if Ps is in a zone E to F inFIG. 6, because this means that load is smaller than the operationcapacity, the operating frequency is decreased. The lower limit of theoperating frequency is to be the lower-limit frequency of 30 Hz of thepreset operating frequency range. If the operating frequency becomesequal to or less than A, namely, Ps×A during operation, the compressor 1a is stopped.

If Ps is in a range of PsD≦Ps≦PsU, in other words, if Ps in zone D inFIG. 6, this means that the operating frequency is at optimum, theoperating frequency at the moment is maintained.

The operation flow chart of the constant-speed compressors 1 b and 1 ccontrolled by the multi controller 9 will be described with reference toFIGS. 3A, 3B, 4 and 5A to 5C. First, a starting control of theconstant-speed compressors while the compressor 1 a is in operation willbe explained with reference to FIG. 3A. If Ps is in a range of PsU<Ps<C,namely, in zone C in FIG. 6 and after the operating frequency of thecompressor 1 a has reached the maximum frequency, the inverter-drivencompressor 1 a has continued operating at the maximum frequency forlonger than a preset time (capacity-up detection time), then a decisionis made that load is heavy and one constant-speed compressor, either 1 bor 1 c, is put into operation to increase the operation capacity.

If the same condition still continues, another constant-speed compressoris put into operation. Even if the operating frequency is not at itsmaximum, if there is a sudden increase in load relative to the currentoperation capacity and Ps is higher than the value C, namely, in thezone A or B in FIG. 6, one constant-speed compressor is put intooperation regardless of the operating frequency. In this way, it ispossible to secure a follow-up characteristic to respond to a suddenchange in load.

Next, a stopping control of the constant-speed compressors while thecompressor 1 a and the constant-speed compressors 1 b and 1 c are inoperation, will be explained with reference to FIG. 4. If Ps<PsD, thatis to say, if the state of the zone E in FIG. 6 continues for aspecified period of time, five minutes or longer for example, then adecision is made that the load is small and one of the constant-speedcompressors 1 b and 1 c is stopped to decrease the operation capacity.If the same state continues further, another constant-speed compressoris stopped, leaving only the compressor 1 a to operate. Even if thestate of Ps<PsD does not continue for five minutes or longer, when theload decreases suddenly relative to the current operation capacity andPs falls to the value B or less, in other words, to the zone F in FIG.6, one constant-speed compressor is stopped. In this way, like in thecapacity-up operation mentioned above, a follow-up characteristic inresponse to an abrupt change in load can be secured.

When Ps is in a range of PsD≦Ps≦PsU as shown in FIG. 3B, an optimumoperating capacity is being obtained and the number of the compressorscurrently in operation may be maintained.

After all compressors were stopped, if there is a large load beforestartup and Ps≧C+0.05 MPa, more specifically, if Ps is in the zone B inFIG. 6, all the compressors 1 a, 1 b and 1 c are started together at thesame time, as shown in FIG. 5A.

When C≦Ps<C+0.05 MPa, that is, when Ps is in the zone B in FIG. 6, twocompressors, more specifically, the compressor 1 a and theconstant-speed compressor 1 b or 1 c are started at the same time, asshown in FIG. 5B.

When PsU<Ps<C, that is, when Ps is in the zone C in FIG. 6, stoppage ofthe constant-speed compressors is maintained and only the compressor 1 ais started, as shown in FIG. 5C. Arranged in this manner, even atcompressor startup immediately after Ps has risen following stoppage ofthe refrigerating cycle for an extended time for defrosting, forexample, an improved follow-up characteristic with respect to load canbe obtained. It ought to be noted, however, that if two compressors arestarted practically simultaneously, a starting current increases to alarge amount and therefore it is desirable to start the compressors oneby one with a time lag of five seconds there between.

Referring to the flow chart in FIG. 8, description will be made ofcontrol of decreasing the operating frequency temporarily beforestarting the constant-speed compressor 1 b or 1 c.

When the operating frequency of the compressor 1 a controlled by theinverter 8 has reached a maximum value and thus the condition forstarting the constant-speed compressor 1 b or 1 c is met, a start-bypassvalve is turned ON to start the constant-speed compressor. After passageof 20 seconds following turning ON of the bypass valve, the operatingfrequency of the compressor 1 a is decreased to a preset operatingfrequency.

How much the frequency is to be decreased is decided by a differencebetween Ps and PsU when the condition for starting the constant-speedcompressor is established. More specifically, when the differencebetween Ps and PsU is smaller than a preset value α, the operatingfrequency is decreased to the lower-limit of the frequency control rangeis used to minimize the change of the operation capacity to therebyreduce energy consumption. When the difference between Ps and PsU islarger than the preset value α, the operating frequency is set to anintermediate frequency of the operation control range to secure afollow-up characteristic with respect to load. After this, the startbypass is turned OFF and the constant-speed compressor is started toshift to ordinary control. With the arrangement described, even if thenumber of compressors to operate is changed, there is not a large changein the operation capacity, in other words, a fine capacity control ismade possible.

Referring to FIG. 7, operation when the inverter is out of order will bedescribed.

When the inverter 8 is normal, electromagnetic contactors 11 and 12 areclosed to conduct electric power to an electric motor 10 for the scrollcompressor 1 a. When any abnormality is detected, such as an abnormalrise in temperature of the inverter 8, the inverter 8 issues anabnormality signal to the unit controller 7. Further, a current detector14 is provided on the secondary side of the inverter 8 to defectcurrents of the motor and in cases such as when the unit controller 7 issending an operation command to the inverter 8 but the current detector14 detects no current, a decision is made that this is a failure.

If a decision is made that there is abnormality or a failure, theelectromagnetic contactors 11 and 12 are opened and an electromagneticcontactor 13 is closed to conduct commercial power directly to the motor10 for the scroll compressor 1 a.

The operating conditions for the scroll compressor 1 a are as follows.If Ps>PsU, the operation of the scroll compressor 1 a is started, and ifPs≦A, the scroll compressor 1 a is stopped. The constant-speedcompressors 1 b and 1 c continue to operate at the same control value aswhen there is no abnormality. Therefore, frequency control is notperformed but stepwise capacity control is possible, so that thecompressors continue to operate.

As has been described, with a refrigerating unit that performs capacitycontrol by changing the revolution speed of the scroll compressors andthe number of units to operate, it is possible to operate therefrigerating unit to provide a capacity which finely matches with theload, so that reductions in energy consumption can be achieved.

Where there are sudden changes in load, a sufficient follow-upcharacteristic with respect to varying load can be achieved by turningthe constant-speed compressors on and off regardless of the operatingfrequency of the scroll compressor controlled by the inverter.

According to the embodiments of the present invention, because a scrolltype inverter-driven compressor is started first, a smooth starting ofoperation in accordance with load can be obtained, and thereafter thedriving frequency of the inverter-driven compressor and the number ofconstant-speed compressors to operate are decided based on the suctionpressure of the compressors. Therefore, even if load varies to a greatdegree, a sufficient capacity can be secured in response to it, and finecapacity control can be implemented. Accordingly, it is possible toperform operation such that the operating capacity is optimum withrespect to load, and reduce energy consumption.

According to the embodiments of the present invention, when the suctionpressure of the compressor is higher than a predetermined value at thestart of operation, the inverter-driven compressor and theconstant-speed compressors are started. Therefore, a sufficientoperating capacity can be secured with respect to load when starting thecompressors, and a smooth response can be obtained to respond to asudden increase in load when it occurs.

Further, according to the embodiments of the present invention, becausethe driving frequency of the inverter-driven compressor and the numberof constant-speed compressors to operate are decided based on a suctionpressure value and the capacity control range has been made so wide as15% to 100%, so that the operating capacity can be made optimum withrespect to a conceivable load of an air conditioner, by which energyconsumption can be reduced.

Further, according to the embodiments of the present invention, evenwhen the inverter becomes out of order, capacity control is continued bychanging the number of compressors in operation, including theinverter-driven compressor and the constant-speed compressors, and evenif frequency control is not performed, stepwise capacity control can becarried on.

Further, according to the embodiments of the present invention, becauseof that when the suction pressure value (Ps) is higher than a presetvalue (PsU), the inverter-driven compressor is started first and thatwhen the suction pressure value becomes higher than a specified value(C), the driving frequency of the inverter-driven compressor isdecreased according to a difference between the suction pressure value(Ps) and the preset value (PsU) and that after the driving frequency hasbeen decreased, the constant-speed compressor is started, even if thenumber of compressors in operation is changed, changes in operatingcapacity can be reduced and therefore a sufficient capacity can besecured to be able to respond to changes in load.

What is claimed is:
 1. A refrigerating unit having an inverter-drivencompressor using a variable driving frequency, and constant-speedcompressors using a constant driving frequency, said refrigerating unitcomprising: a pressure sensor installed on the suction side of theinverter-driven compressor and said constant-speed compressors; meansfor starting said inverter-driven compressor first, and means fordeciding a driving frequency of said inverter-driven compressor or thenumber of the constant-speed compressors to operate, based on a suctionpressure value detected by said pressure sensor after said inverterdriven compressor is started, wherein when said suction pressure valuerises above a specified value, one or more of said constant-speedcompressors is started regardless of the driving frequency of saidinverter-driven compressor.
 2. A refrigerating unit according to claim1, wherein when the suction pressure value falls below a specifiedvalue, said constant-speed compressors are stopped regardless of thedriving frequency of said inverter-driven compressor.
 3. A refrigeratingunit according to claim 1, wherein said constant-speed compressors arestarted one by one after the driving frequency of said inverter-drivencompressor has reached the maximum value.
 4. A refrigerating unitaccording to claim 1, wherein said constant-speed compressors arestopped one by one after the driving frequency of said inverter-drivencompressor has reached the minimum value.
 5. A refrigerating unitaccording to claim 1, wherein the maximum and minimum values of thedriving frequency of said inverter-driven compressor are set, and saidconstant-speed compressors are started one by one after the maximumfrequency has been reached, and said constant-speed compressors arestopped one by one after the minimum frequency has been reached.
 6. Arefrigerating unit according to claim 1, wherein said inverter-drivencompressor and said constant-speed compressors are of scroll type,wherein when a value detected by said pressure sensor at starting thecompressor is greater than a preset value, said inverter-drivencompressor and said constant speed compressors are started, andthereafter the driving frequency of said inverter-driven compressor andthe number of constant-speed compressors to operate are decided.
 7. Arefrigerating unit according to claim 1, wherein said inverter-drivencompressor and said constant-speed compressors are of scroll type,wherein the driving frequency of said inverter driven compressor and thenumber of constant-speed compressors to operate are decided based on asuction pressure value detected by said pressure sensor and the capacitycan be controlled in a range of 15% to 100%.
 8. A refrigerating unitaccording to claim 1, wherein said inverter-driven compressor and saidconstant-speed compressors are of scroll type, said refrigerating unitfurther comprising: means for determining a failure of an inverter fordriving said inverter-driven compressor, wherein when said inverter isdetermined to be out of order by said failure-determining means,operating capacity control is continued by changing the number ofcompressors operating, including said inverter-driven compressor andsaid constant-speed compressors.
 9. A refrigerating unit according toclaim 1, wherein said inverter-driven compressor and said constant-speedcompressors are of scroll type, said means for starting starts theoperation of said inverter-driven compressor when a suction pressurevalue (Ps) detected by said pressure sensor is greater than a presetvalue (PsU); said means for decreasing decreases the driving frequencyof said inverter-driven compressor according to a difference between thesuction pressure value (Ps) and the preset value (PsU) when the suctionpressure value has risen above a specified value (C) after saidinverter-driven compressor is started; and said refrigerating unitfurther comprising means for starting a constant-speed compressor afterthe driving frequency was decreased.
 10. A refrigerating unit,comprising: an inverter driven compressor having a variable drivingfrequency; at least one or more constant speed compressors; a pressuresensor installed on the common suction side intake of the inverterdriven compressor and the at least one constant speed compressor todetect suction pressure; and a controller connected to the inverterdriven compressor, the at least one or more constant speed compressorsand the pressure sensor, wherein the controller activates the inverterdriven compressor first and then the at least one or more constant speedcompressors are activated based solely upon the suction pressure beingabove a predetermined value and said activation of the at least one ormore constant speed compressors being completely independent of thedriving frequency of the inverter driven compressor.
 11. Therefrigerating unit recited in claim 10, wherein the controllerdeactivates the at least one or more constant speed compressors when thesuction value falls below a predetermined value, said the activation iscompletely independent of the driving frequency of the inverter drivencompressor.
 12. The refrigerating unit recited in claim 10, wherein thecontroller after activating the at least one or more constant speedcompressors determines the driving frequency of the inverter drivencompressor to optimize operating capacity of the refrigerating unit. 13.The refrigerating unit recited in claim 10, wherein to the one or moreconstant speed compressors further comprises: a first constant speedcompressor; a second constant speed compressor, wherein the controlleractivates the first constant speed compressor based upon the suctionpressure and then activates the second constant speed compressor basedupon only suction pressure, the activation of the first constant speedcompressor and the suction constant speed compressor are independent ofthe driving frequency of the inverter driven compressor.